This invention relates to document copiers and, more particularly, to a method and apparatus for improving images produced by such copiers, through use of digital processes.
The prior art includes many teachings directed to methods for the improvement of copier image outputs. Such methods cover a wide variety of complex algorithms that involve different combinations of different image processing techniques. Such techniques include edge-detection, pixel smoothing, pixel sharpening, scaling through resolution conversion, and halftoning using one or more dithering techniques. Typically, prior art halftoning techniques have involved simple thresholding, error diffusion or xe2x80x9cdevice-bestxe2x80x9d cluster dither actions. All of such actions require significant tradeoffs, including user selection of good text/good pictures, complex processing and the use of large buffers for wide area processes and high resolution scanning.
Any system that is intended to be used to improve the quality of scanned images in a copier must deal with a number of potential variables, i.e., halftoned originals, scanned text, a limited printer gamut, unknown black and white values in the original document, etc. Further, any method employed to improve digital image presentation in a copier""s document output needs to address the process variables automatically and dynamically so as to enable high quality copies, with high throughput.
Accordingly, it is an object of this invention to provide an improved method and apparatus for maximizing copy quality in a digital copier.
It is another object of this invention to provide an improved method and apparatus for handling digital images in a pipeline fashion, while simultaneously providing improved, higher resolution image documents.
It is yet another object of this invention to provide an improved method and apparatus for handling images that assures improved output image quality.
The method of the invention improves the presentation of pixel data images in output documents. The method is implemented by a pipeline of image processing actions which, among others, includes an edge evaluation step wherein neighborhoods of pixel data are examined to derive edge values that are indicative of an edge presence in the respective neighborhood. Each edge value is further indicative of the intensity of the edge. The edge evaluation action further determines scaling parameters which enable later distribution of a neighborhood""s center pixel tone value to subpixels that are created during a scaling action of the center pixel. The method then applies an interpolated value between plural tone correction values to the center pixel value, with the interpolation is dependent upon the edge intensity value derived for the center pixel""s neighborhood. The method then scales the center pixel to a higher level of resolution and, through use of the previously derived scaling parameters, distributes the pixel""s tone value to the higher resolution subpixels. The method further employs a halftoning procedure so that pixel neighborhoods having no edge are subjected to a halftone procedure that mimics the scaling procedure, but utilizes predetermined distribution parameters to enable appropriate placement of the halftone dots.